1. Field of the Invention
The invention relates to a method for automatically detecting at least one printing plate edge in at least one clamping device of a plate cylinder of a printing press, the presence or absence and/or the position of a printing plate edge in the at least one clamping device being detected by at least one sensor.
The invention relates, furthermore, to a device for performing the foregoing method, with at least one sensor disposed in a clamping device of a plate cylinder and constructed for detecting the presence or absence and/or the position, respectively, of a printing plate edge in the at least one clamping device, and with at least one transmitter for transmitting the signals from the plate cylinder to stationary parts of the printing press.
When printing plates were still clamped onto plate cylinders of printing presses by hand, it was also possible to detect visually whether a printing plate edge, i.e., a trailing or a leading edge, was located in the clamping device provided for the purpose, or whether the edge was completely removed from the latter. The person involved could sometimes even detect the position of a printing plate edge in the clamping device purely by feeling or instinct. It was consequently possible to prevent damage to the printing press or to the printing plates that may occur due to errors in clamping or unclamping. With the advent of automatic clamping devices, this control or check became more difficult and, due to semiautomatic or fully automatic printing plate feeding and printing plate removal devices, it is often barely possible any more, because these devices are located in front or upline of the clamping devices.
The published European Patent Document EP 0 551 976 B1 presents a proposal of the type mentioned in the introduction hereto, but it is restricted to arranging sensors only at the leading edge clamping device, in order to detect the presence or absence and the position of the leading edge of the printing plate. This check or control is insufficient, however, because the clamping of the trailing edge must also be checked when the printing plate is being clamped. Even when the printing plate is unclamped, it is necessary to detect the clamping of the printing plate trailing edge. Only when the printing plate trailing edge has left the clamping device, is it possible for the plate cylinder to continue to rotate, and thereby unwind the printing plate and then unclamp the leading edge, without any risk of damage to the printing plate and/or the printing press. If malfunctions should occur and remain unnoticed during the aforedescribed operations, damage to the printing plate or to the printing press may occur during the further progress of the clamping or unclamping operations or at the start of printing. It is possible, for example, that the trailing edge may become released at a wrong instant of time and, when the rotating plate cylinder strikes against the blanket cylinder, inking rollers or other parts and damages them and, naturally, also the printing plate is damaged or destroyed.